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Fig Psyllids - fact sheet
The Fig Psyllid (Mycopsylla fici) is responsible for periodic defoliation of Moreton Bay Fig trees (Ficus macrophylla). These psyllids are small insects which live in colonies and produce a protective sticky ‘lerp’ or cover, under which they live. The lerp is constructed communally from wax and honeydew excreted by the psyllids as they feed and can be up to 35mm wide. The lerp protects the psyllid from changing weather and from attacks by natural enemies. Given the right conditions, psyllid populations can build up in large numbers, and the tree can be quite damaging.
Life Cycle: Adult psyllids are winged insects which fly between leaves in search of mates, food, and egg-laying sites. The female psyllid will lay small orange-brown eggs 0.5 mm in diameter, in tightly-packed clusters of up to 50 eggs per cluster, on the margins of the leaf. Occasionally, they may be found near the mid-vein or the centre of the leaf blade. Females can lay a number of egg clusters. Eggs within a cluster will hatch simultaneously, the wingless juvenile psyllids (nymphs) emerging and walking a short distance across the leaf where they settle down to feed in a group. As the psyllid nymphs feed, they excrete honeydew (water and unused plant sugars) and two sets of waxlike filaments. The honeydew fills up the spaces between the curling filaments, forming the lerp. The nymphs moult progressively until they reach the preadult stage, at which point they emerge from under the lerp and undergo their final moult to become adults, anchoring themselves to the leaf tissue while the moult takes place. After expanding their wings, the adults feed and fly off in search of mates. In the earlier stages of lerp formation, the lerp is vulnerable to moisture, being mostly a dehydrated sugar solution: the lerp absorbs water, and starts to flow over the leaf. While this deprives the psyllids their protective covering, it has consequences for the leaf, since the flowing sugar solution blocks the leaf’s breathing pores, thus (it is thought) suffocating the tissue underneath.
Damage: Psyllids can cause the trees to totally defoliate, but usually the damage is less. The greater the psyllid load, the greater the defoliation can be. The lerp can play a major part in this defoliation, possibly by the blocking of leaf breathing pores mentioned above. The side effects of leaf loss are a reduction in plant nutrition, and sunburn on the bare branches. When these effects occur in conjunction with other stressful events such as drought, soil compaction or root disturbance (or a combination of these), severe and sometimes permanent disruption of the tree may result. Weakened trees are also much more susceptible than healthy trees to attack by other insects such as borers and termites, and pathogenic fungi.
Chemical Control: The use of pesticides is unacceptable because of the broad spectrum of insects and spiders affected (including beneficial ones), the large amounts of insecticide needed to treated a single tree and the consequent high risk of off-target spray drift. Injection of systemic insecticides into the trunks of figs will badly damage the figs both by the drilling process and invasion of pathogens through the injection holes.
Biological Control: The young psyllid is attacked by a number of natural enemies. It is parasitised by a wasp (Psyllaephagus sp.); the female adult wasp lays an egg into the psyllid nymph before the lerp becomes impenetrable to the wasp, the wasp larva hatches and develops inside the living psyllid nymph. The psyllid nymph is killed when the wasp pupates to become an adult. It is important to mulch fallen psyllid-affected leaves near trees so that the wasp can emerge and continue to parasitise psyllids. Lacewing and ladybird larvae also feed on the psyllid nymphs. Birds, particularly swallows, have been observed flying around fig trees when adult psyllids are numerous, and eat adult psyllids. Web-spinning spiders account for a large number of adults.
Scientific research at the Royal Botanic Gardens & Domain Trust is being conducted on the psyllid problem, with the ultimate aim of developing an integrated management strategy for the fig trees. Knowledge of the psyllid and its natural enemies, and other factors involved in the ecology and urban cultivation of Moreton Bay figs, acquired during this project, will enable us to better understand the psyllid and hence to control it.